In motors such as brushless motors, in general, a rotor (a rotor) including magnets for generating magnetic fields rotates inside a stator (a stator) having coils (windings). This stator mainly includes a cylindrical stator core (a stator core) having a plurality of tooth portions (magnetic teeth) which protrude therefrom radially inwards and slots (iron core slots) which are defined between the adjacent tooth portions and coils which are disposed around the respective tooth portions. Here, an insulator made of a resin (an insulating material) is attached to the coils for isolating the coils from the stator core.
In a motor like this, there is a strong demand for an increase in space factor (winding density) of the coils in the stator in order to realize miniaturization and an increase in turning effort (response) of the motor, and coils turned as many as possible need to be disposed around the respective tooth portions.
Should an attempt be made to provide a coil in a multiplicity of layers on the circumference of each tooth portion through the insulator, however, a force comes to act more strongly which attempts to cause an upper coil to divide a lower coil. Namely, in this case, as is shown in FIG. 6A, a winding 13a of an upper layer forcibly squeezes itself between a winding 13a of a lower layer, and a force comes to act more conspicuously which attempts to forcibly open the winding 13a of the lower layer radially inwards and outwards of a stator 1′.
As this occurs, as is shown in FIG. 6A, since an annular portion 2a of a stator core 2′ exists radially outwards of the stator 1′, a winding displacement of the coil 13 which is directed radially outwards is stopped by the annular portion 2a, and a winding displacement of the coil 13 is then generated to be directed radially inwards (the coil 13 comes to be wound thicker in the vicinity of a center of the stator core 2′). As a result, the proper arrangement of the winding is disturbed, and a dead space (a space in which the coil 13 does not exist) is formed in an interior of each slot 12 (refer to FIG. 1), which results in a reduction in space factor of the coil 13. As this occurs, as the winding 13a is wound in more layers, a squeezing amount of the winding 13a of the upper layer into the winding 13a of the lower layer becomes larger, and in conjunction with this, the winding displacement of the coil 13 directed in a radially inward direction of the stator 1 is also increased.
On the other hand, there has been known a technique in which the number of turns of a coil at a root portion of every other tooth portion is increased so as to cause the coil to have a swollen shape (refer to JP-A-2004-104870).
According to this technique, in order to increase the number of turns of the coil at the root portion of every other tooth portion so as to cause the coil to have the swollen shape, firstly, a winding coiling nozzle (needle) is inserted in advance within a slot so as to form a coil of winding on every other tooth portion, and the nozzle is turned in many times to wind the windings at the root portion side of the tooth portion so as to swell the coil. Thereafter, the nozzle is pulled out of the slot and is then operated to loop around an adjacent tooth portion in the vicinity of a slot entrance portion (an open slot). Then, by the winding being caused to slide along a tapered portion of the coil, the coil can be formed without inserting the nozzle into a deep portion of the slot.
Namely, according to the technique, a dead space necessary for insertion of the nozzle in the interior of the slot is made unnecessary, whereby the space factor of the coil is increased. In other words, the winding can be coiled on a tooth portion interposed between the alternate tooth portions at the slot entrance portion without interfering with the adjacent coil, and the interior of the slot including the deep portion thereof can be made effective use of as a coil forming area, thereby making it possible to increase the space factor in theory.